U.S. patent application number 15/410206 was filed with the patent office on 2017-05-11 for monolithic element and system for collimating or focusing laser light from or to an optical fiber.
The applicant listed for this patent is Kaiser Optical Systems Inc.. Invention is credited to James M. Tedesco.
Application Number | 20170131478 15/410206 |
Document ID | / |
Family ID | 55267282 |
Filed Date | 2017-05-11 |
United States Patent
Application |
20170131478 |
Kind Code |
A1 |
Tedesco; James M. |
May 11, 2017 |
MONOLITHIC ELEMENT AND SYSTEM FOR COLLIMATING OR FOCUSING LASER
LIGHT FROM OR TO AN OPTICAL FIBER
Abstract
A monolithic optical element and system is used for collimating
or focusing laser light from or to optical fibers. The optical
fiber terminates in a tip that directly abuts against the first
surface of the optical element. The optical element may provide a
collimation or focusing function depending upon whether the
abutting fiber delivers light for collimation or receives focused
light from a collimated beam. The optical element may be a standard
or modified barrel or drum lens, with the first and second surfaces
being convex curved surfaces having the same or different radii of
curvature. The end of the optical element to which the fiber abuts
may have a diameter to match the inner diameter of a ferrule for
positioning the fiber. A pair of the elements may be used for
collimation and focusing in a Raman probehead or other optical
detection system.
Inventors: |
Tedesco; James M.; (Livonia,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kaiser Optical Systems Inc. |
Ann Arbor |
MI |
US |
|
|
Family ID: |
55267282 |
Appl. No.: |
15/410206 |
Filed: |
January 19, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14455235 |
Aug 8, 2014 |
|
|
|
15410206 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4201 20130101;
G02B 6/3624 20130101; G02B 6/3869 20130101; G02B 3/0087 20130101;
G01J 3/44 20130101; G01J 3/0218 20130101; G02B 6/32 20130101; G02B
3/02 20130101; G01J 3/0208 20130101; G01J 3/0205 20130101; G02B
6/322 20130101; G01J 3/024 20130101 |
International
Class: |
G02B 6/32 20060101
G02B006/32; G01J 3/44 20060101 G01J003/44; G01J 3/02 20060101
G01J003/02; G02B 6/42 20060101 G02B006/42; G02B 6/36 20060101
G02B006/36 |
Claims
1. An optical system adapted for use with an optical fiber having a
tip, consisting of: a monolithic, homogenous glass optical element
defining an optical axis with opposing first and second end
surfaces, wherein the tip of the optical fiber is butted up
directly against one of the surfaces of the optical element
providing a light-collimating or light-focusing function.
2. An optical measurement probehead configured for interconnection
to a first optical fiber for carrying excitation energy to the
probehead, and a second optical fiber for carrying collected energy
from the probehead for analysis, the probehead comprising: a first
monolithic optical component having an incident surface for
receiving light from an end of the first optical fiber and a
transmission surface outputting an expanded, collimated excitation
beam for direction to a sample; a beam combiner for merging a
collimated collection beam from the sample with the collimated
excitation beam to produce a counter-propagating combined beam; and
a second monolithic optical component having an incident surface
for receiving the combined beam and a transmission surface
structured to output a focused beam into an end of the second
optical fiber, wherein an end of the first optical fiber butts up
directly against the incident surface of the first monolithic
optical component and the end of the second optical fiber butts up
directly against the transmission surface of the second monolithic
optical component.
3. The optical probehead of claim 2, wherein both optical
components are barrel or drum lenses.
4. The optical probehead of claim 2, wherein both optical
components are identical barrel or drum lenses.
5. The optical probehead of claim 2, wherein ends of the first
monolithic optical component and the second monolithic optical
component to which the optical fibers butt up against have
diameters to match the outer diameter of a ferrule receiving the
respective optical fibers.
6. The optical probehead of claim 2, wherein the excitation and
collection beams are respectively configured to induce and collect
Raman scattering from the sample.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a divisional application of U.S.
patent application Ser. No. 14/455,235, filed on Aug. 8, 2014, the
entire contents of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] This invention relates generally to optical systems and, in
particular, to a monolithic optical element and system for
collimating or focusing laser light from or to optical fibers in a
Raman or other optical measurement probe, for example.
BACKGROUND
[0003] FIG. 1 is a simplified schematic diagram illustrating
imaging optics used to collimate the light from an optical fiber
104. As is typical, the distal end of the fiber is spaced apart
from the surface of lens 102 used for collimation. Not only does
this arrangement require precise mechanical locating (and
re-locating) to laterally and axially align the fiber relative to
the lens, if the fiber is carrying high-power laser light, as might
be the case with Raman probes, this results in a high energy
density in the air space between the tip of the fiber and the
imaging optics. As a result, couplings of this kind must be sealed
and/or purged to meet safety or environmental requirements.
BRIEF SUMMARY
[0004] This invention relates generally to optical systems and, in
particular, to a monolithic optical element and system for
collimating or focusing laser light from or to optical fibers. Such
a system includes a monolithic, homogenous glass optical element
defining an optical axis with opposing first and second end
surfaces. An optical fiber, terminating in a tip, is butted up
against the first surface of the optical element to make intimate
physical contact therewith.
[0005] The optical element may provide a collimation function by
receiving light from the tip of the fiber and transmitting the
light as a collimated beam from the second surface, or the element
may provide a focusing function by focusing a collimated beam
incident on the second surface to the tip of the fiber. The light
being collimated or focused is confined substantially within the
optical element, thereby eliminating the presence of high energy
density light in any gap between the tip of the fiber and the first
surface of the optical element where it may come into contact with
combustible gases and potential contaminants.
[0006] The optical element may be a barrel or drum lens, with the
first and second surfaces being convex curved surfaces having the
same radius of curvature. Alternatively, the radius of curvature of
the first surface may be different than the radius of curvature of
the second surface, or even flat, to minimize mechanical stress
concentration at the point of contact between the fiber ferrule and
the lens. The length of the lens is chosen in conjunction with the
refractive index of the lens material and the distal surface radius
in order to generate zero back focal length, that is, perfect
collimation out, or focusing of collimated light in, with the fiber
in contact with the lens.
[0007] The optical element may alternatively be constructed in the
form of a gradient index (GRIN) lens of appropriate length to
produce the same effect of collimation or focusing with a fiber in
optical contact, as is commonly practiced in devices for fiber
optic telecommunications. With a GRIN lens, a spatial refractive
index gradient performs the light bending instead of a curved
air/glass interface. However, commonly available GRIN materials and
lenses are only available in a very limited range of diameters,
focal lengths and numerical apertures, making their adaptation to
optical measurement probe designs impractical without major
investment in custom GRIN lens design and fabrication.
[0008] The end of the optical element including the first surface
has a diameter to match the inner diameter of a connector ferrule
carrying the optical fiber. The system may include two of the
optical elements, one acting as a light collimator, and the other
acting as a light focusing element in a Raman measurement
probe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 s a simplified schematic diagram illustrating
prior-art imaging optics used to collimate the light from an
optical fiber;
[0010] FIG. 2 is a simplified diagram illustrating a basic
embodiment of the invention in a light collimating
configuration;
[0011] FIG. 3 is a simplified drawing that illustrates a different
embodiment of the invention utilizing a modified barrel or
drum-type lens as a monolithic optical element;
[0012] FIG. 4A is a cross section of an existing Raman probe
manufactured by Kaiser Optical Systems of Ann Arbor, MI to which
the invention is applicable;
[0013] FIG. 4B is an exploded view of the probe configuration of
FIG. 4A; and
[0014] FIG. 5 is a detail drawing of a monolithic optical component
applicable to the probe of FIG. 4 with dimensions.
DETAILED DESCRIPTION
[0015] This invention broadly uses a monolithic optic element to
collimate or focus from/to an optical fiber with multiple
advantages, including:
[0016] 1) the elimination of high energy density hot spots and the
components and assembly steps required for sealing and/or
purging;
[0017] 2) the elimination of various optical components as well as
the machining required to hold and position such components in a
housing; and
[0018] 3) a dramatic reduction in the requirements for axial and
lateral alignment of the fiber relative to the monolithic optic
element, thereby simplifying fiber locating and relocating
procedures.
[0019] FIG. 2 is a simplified diagram illustrating a basic
embodiment of the invention in a light collimating configuration.
The monolithic optic element 202 in this case may be a standard
barrel or `drum` lens, defined as a cylindrical plug taken from a
glass sphere indicated by the broken-line circle. Such a sphere
section produces most accurate collimation/focusing of a contacted
fiber if the refractive index of the glass is 1.5, with the length
of the lens being exactly twice the radius of each surface
curvature. As such, the radii of the light-receiving and
transmitting surfaces 204, 206 may be the same though not
necessarily as discussed in conjunction with other embodiments
described below, including the use of modified length and glass
refractive index.
[0020] Using the monolithic optic element 202, the distal tip of
optical fiber 208 may be butted up directly against light-receiving
surface 204, thereby confining the high energy density light within
the glass of the lens, eliminating hot spots that may otherwise be
exposed to potential contaminants, condensates, or hazardous
environments. The collimated beam emerging from the glass is of
sufficiently low energy density to avoid the necessity of
purging/sealing for safety reasons. Any appropriate assembly
technique may be used to maintain the relative relationship of the
fiber/lens. For example, particularly if element 202 is a straight
cylinder with positioning shown, it may be potted into an assembly
with a precision bore to receive a fiber ferrule. Other techniques
may alternatively be used as described below. In a preferred
embodiment, the lens and fiber ferrule may be mated with
inexpensive fiber mating spring sleeves that are mass-produced for
the telecommunications industry. The reader will appreciate that
the configuration of FIG. 2 may be used for focusing purposes with
surface 206 receiving incident collimated light that is focused
onto the tip of a fiber with surface 204 acting as the transmitting
side.
[0021] FIG. 3 is a simplified drawing that illustrates a slightly
different embodiment of the invention. In this case, monolithic
optic element 302 departs further from a standard drum lens of FIG.
2. In particular, the element length is matched to the refractive
index of the glass and the distal surface radius to ensure that
contact with the optical fiber generates precise collimation (or
focusing, as the case may be). Use of higher refractive index glass
serves to minimize spherical aberration for a given effective focal
length and numerical aperture. This, along with the fact that there
is no air-glass interface to introduce aberration at the fiber end,
can eliminate the necessity to use an expensive aspheric surface as
is employed in the more traditional configuration of FIG. 1.
[0022] The element 302 further includes a stepped-down end 304 to
match the diameter of a standard fiber ferrule 306 (a very
inexpensive split cylindrical spring that provides ideal location
and centering of the fiber 308 relative to the element 302). The
stepped diameter allows generation of a longer focal length and
larger collimated aperture relative to available cylindrical GRIN
lenses and standard fiber ferrule/sleeve diameters. This can be
required to reduce beam divergence, particularly with multimode
fibers. Another departure is that the radius of surface 308 is not
necessarily the same as that of surface 310. In fact, surface 308
may be flat by virtue of the intimate contact with the fiber 308;
but instead, this surface is slightly curved to ensure reliable
contact, but not so curved as to generate undesired stress that may
chip the glass.
[0023] FIG. 4A is a cross section of an existing Raman probe
manufactured by Kaiser Optical Systems of Ann Arbor, MI to which
the component of FIG. 3 is applicable. Such a probe is described in
U.S. Pat. No. 6,907,149, entitled Compact optical measurement
probe, the entire content of which is incorporated herein by
reference. Excitation illumination is brought into the probe over
fiber 402, which is then collimated by lens 404. The collimated
light then passes through a bandpass filter 408 to remove the
non-laser wavelengths generated en route from the source. The
filtered light is reflected by a mirror 406 onto a beam combiner
420 which is then directed to a sample `S` along a
counter-propagating optical path 422. The light scattered by the
sample thus returns along path 422, passes through beam combiner
420 in the reverse direction, and is filtered by an optional notch
filter 416 before being focused by lens 414 onto the end of
collection fiber 412.
[0024] FIG. 4B is an exploded view of the probe configuration of
FIG. 4A. The assembly further includes fiber input windows 422,
dowel pins 428, "bat-wing" spring 426 to locate fiber optic
ferrules (not shown), and modified dowel 428. FIG. 5 is a detail
drawing of a monolithic optical component 500 applicable to the
probe of FIG. 4 with dimensions. Optional relief region 502 is
provided to ensure that the ferrule (not shown) "sees" a flat
surface as opposed to a chamfer. Use of component 500 in the probe
of FIG. 4 for both collimation and focusing functions eliminates
windows 422, dowel pins 428, spring 426 and (aspheric) lenses 404,
414 for a significant reduction in parts count and manufacturing,
alignment and maintenance costs.
* * * * *